Method of making lithographic printing plate and photopolymer composition

Abstract

A method of making a lithographic printing plate by forming images at the surface of a lithographic printing plate precursor by means of a thermal head, with the lithographic printing plate precursor having on a support a recording layer comprising a polymer having at least either carboxylic acid or carboxylate groups capable of causing thermal decarboxylation; and a photopolymer composition for recording by exposure to infrared laser beams, wherein a thermally decarboxylation-causing polymer and a photothermal converter are comprised.

What is claimed is:  
     
       1. A photopolymer composition for recording images by exposure to infrared laser beams, said composition comprising a photothermal converter and a thermal decarboxylation-causing polymer that comprises at least either constitutional repeating units represented by the following formula (1) or constitutional repeating units represented by the following formula (2):                    
       wherein X represents a group 4, 5 or 6 element, an oxide thereof, a sulfide thereof, a selenide thereof or a telluride thereof; P represents a repeating unit constituting the polymer main chain; —L— represents a divalent linkage group; R 1  and R 2 , which are the same or different, each represent a hydrogen atom or a monovalent group; and M represents an alkali metal, an alkaline earth metal or an onium.